Typical fluid mass flow control valves or so called mass flow controllers of the type useful in the semiconductor manufacturing industry are required to be relatively precise instruments. Known types of fluid mass flow controllers are typically constructed by machining the valve body from a solid block of corrosion resistant dense metal. This type of fabrication results in the significant removal of material to generate the flow passages and mounting details for the valve seat and actuator and seals required to isolate the valve components from the gas flow stream. After the significant amount of machining required in prior art fluid mass flow controllers, the machine finished parts are required to be mechanically and electro polished to improve surface finish and corrosion resistance.
Still further, certain known types of fluid mass flow controllers utilize so called thermal actuators which are adapted to effect movement of a valve closure member by flexing a mechanical diaphragm connected to a branch tee or similar conduit part of the valve body. However, this type of construction is relatively expensive, complicated and produces uniform elastic deflection of a link connected to the closure member in all directions. Moreover, certain prior art types of fluid mass flow controllers utilize a thermal actuator comprising a hollow tube sealed at both ends and placed in the fluid flow stream. This arrangement complicates the control function since the temperature of the actuator tube is influenced by the flow of fluid (gas) which it is controlling. These arrangements typically result in slow response time required to reach a steady state flow for the controller. Still further, with prior art fluid mass flow controllers, the maximum displacement of the actuator is significantly affected by the specific gas that is being controlled by the controller. However, the present invention provides a fluid mass flow control valve and method of operation which overcomes several disadvantages of prior art fluid mass flow controllers.
The present invention provides an improved fluid mass flow control valve or so-called controller and method of operation. In particular, the invention provides a fluid mass flow control valve of a type useful in controlling fluid mass flow in applications in the semiconductor processing industry.
In accordance with one important aspect of the present invention a fluid mass flow control apparatus is provided which utilizes a section of commercially available cylindrical tubing as a valve body and which is subject to relatively minor machining operations to provide a flexible wall portion of the valve body creating a pivot point at which a valve actuator arm is attached and is operable to move a valve closure member for controlling mass flow through the apparatus. The flexible wall portion is configured in such a way that elastic deflection is uniform in the desired directions of movement of the valve actuator arm but the flexible wall portion exhibits greater stiffness to resist deflection in unwanted directions.
In accordance with another aspect of the present invention, an improved fluid mass flow control apparatus is provided which comprises a unique actuator for moving a pivoting control arm operably engaged with a closure member. The fluid mass flow control apparatus utilizes relatively uncomplicated and inexpensive components for construction of the valve body, provides simplified fabrication required to construct the mass flow control apparatus and is adaptable to utilize different types of actuators for moving the actuator control arm. Although a thermal actuator is one preferred type, other types of valve actuators may also be used. Moreover, the actuator is not susceptible to heating or cooling effects of the fluid flowing through the flow control apparatus.
The fluid mass flow control apparatus of the invention also improves the response time for changing the mass flow rate of fluid being controlled by the apparatus. The present invention also provides a method of operation of a fluid mass flow control apparatus which provides more rapid and accurate responses to required fluid mass flow changes.
Those skilled in the art will further appreciate the advantages and superior features of the invention upon reading the detailed description which follows in conjunction with the drawing.